In an oscillation type angular speed sensor having an oscillator, the oscillator oscillates with a predetermined frequency. When an angular speed is applied to the sensor, a Coriolis force is generated in the oscillator so that the oscillator is displaced. The displacement of the oscillator is detected so that the angular speed is detected.
This oscillation type angular speed sensor and an acceleration sensor are mounted on one mounting base such as a circuit chip or a substrate so that a physical quantity sensor is formed. The physical quantity sensor can detect both of the acceleration and the angular speed. However, the oscillation of the oscillator may transmit to the acceleration sensor so that the acceleration sensor is also oscillated even though no acceleration is applied to the sensor. Thus, the detection accuracy of the acceleration sensor is deteriorated. This transmit of the oscillation is a leakage of the oscillation.
To prevent the leakage of the oscillation to the acceleration sensor, the angular speed sensor is sealed in vacuum, and the acceleration sensor is sealed in an atmospheric pressure. In this case, the leakage of the oscillation from the angular speed sensor to the acceleration sensor is reduced by an air damping effect. This type of physical quantity sensor is disclosed in, for example, US Patent Application Publication No. 2002-0051258.
However, since the air damping type physical quantity sensor bas a vacuum sealing construction, a total construction of the sensor becomes complicated. Thus, a manufacturing cost of the sensor becomes higher.